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conversion of extremely saturated photos to cmyk

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  #1  
Old 09-25-2008, 02:17 AM
girlsfather girlsfather is offline
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conversion of extremely saturated photos to cmyk

Here is a question to all the preprint colour-experts:
What is the best way to convert saturated pictures that show aereas that do not fit in the cmyk colourspace from rgb to cmyk ?

I have a very saturated photograph, 16 bit in eci-rgb_v2.icc.
When converting to cmyk, isocoated_v2.icc, in CS3 the background looks awful (colour clipping in the soft colour-gradients
I tried all methods and relative colorimetric is the most pleasant.

The best I found out so far is: Reduce Saturation in CS3 by 40%, that is the amount necessary to avoid clipping.
Then convert to profile.
Then in cmyk increase saturation again.
The attached Photo shows part of the background.

The gradient background keeps smooth with the -40/+40 saturation method.
The colour-change is not really nice.
Is there a better, more professional way?

Thank you for every help!!!

Michael
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File Type: jpg test_conversion.jpg (95.1 KB, 69 views)
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  #2  
Old 09-25-2008, 08:05 AM
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TommyO TommyO is offline
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Re: conversion of extremely saturated photos to cm

Michael,
Will take a look at it. Also, could you post images (or zip) we can actually play with, in another format... the jpeg's get converted to sRGB and loose all relative differences in color. So, it does not do much good to look at those. It would also be better if they were separated, not in one image.

Typically, it is best if you control the conversion/desaturation and not the conversion engine. At least that way you some control over the result. What you're doing is fine, as long as you like the result. Base final result on a hard proof though.
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Old 09-25-2008, 01:45 PM
pixelzombie pixelzombie is offline
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Re: conversion of extremely saturated photos to cm

i have also found that reducing the saturation before your conversion will make a huge improvement in your cmyk file...
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Old 09-25-2008, 02:24 PM
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TommyO TommyO is offline
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Re: conversion of extremely saturated photos to cm

After leaving and thinking, it dawned on me that you really did not describe what your workflow or end result was targeting, i.e. are you trying to profile/match your contract proofer or your press? ...what paper stock? ...is there a color server that can do it for you?

Since presses vary in their output and are expensive to profile, many people profile the contract proofer. It is also generally more successful matching the contract proofer. The colorants used by the proofer are similar to press inks in their dot gain characteristics, etc. Then you end up with separations that work for both, making your workflow easier.

The benefit is being able to set limits on ink and black generation and create separations that ready for the press. Of course, if there is a color server that can do the profile conversions from press to proofer for you, that is ideal. It can make adjustments for the changes in dot gain on differing paper stocks and apply the transfer characteristics for the platesetter or imagesetter. The resulting profile then becomes your aim point for your RGB-to-CMYK conversions and can serve as your proof profile as well.
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Old 09-25-2008, 03:37 PM
girlsfather girlsfather is offline
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Re: conversion of extremely saturated photos to cm

[QUOTE=TommyO;207217]After leaving and thinking, it dawned on me that you really did not describe what your workflow or end result was targeting, i.e. are you trying to profile/match your contract proofer or your press? ...what paper stock? ...is there a color server that can do it for you?

Hi Tommy,

thank you very much for your answers and questions.
I am a professional photographer, doing my own retouching.
I work in Photoshop CS3 with calibrated TFT and custom printer profiles (RGB) for my Epson 4800 to print my portfolio.

This Image is going to be 4c offset-printed for selfpromotion in an exclusive artbook-publication.
My aim is to see the possible result in advance.
So I checked the Numbers and Photoshop tells me that great parts of especially the background is not within the printable colourspace of isocoated_v2.

I normally deliver both - RGB-Files and the converted CMYK.
In this case I have the impression that the Contractproof and later the offsetprint will look awful.
Maybe I am totally wrong?

I am looking to talk to the printing house and their experts.
I want to learn more about conversion from RGB to CMYK, so I posted this question here.

So, do I need to own other applications than photoshop to do the conversion?

Here now a jpg with maximum quality and the eci-rgb_v2 embedded.
Still quite small pic - I do not have a possibility to put a bigger one online.
(This limitation to 100KB seems set a bit too low ;-)))
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File Type: jpg conversion_original_8bit_eci.jpg (86.2 KB, 18 views)
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  #6  
Old 09-25-2008, 03:48 PM
pixelzombie pixelzombie is offline
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Re: conversion of extremely saturated photos to cm

is your epson calibrated for the presshouse that will be printing this book?
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  #7  
Old 09-25-2008, 04:02 PM
girlsfather girlsfather is offline
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Re: conversion of extremely saturated photos to cm

Quote:
Originally Posted by pixelzombie View Post
is your epson calibrated for the presshouse that will be printing this book?
Hi Pixelzombie,

no the printer is profiled to give the best result printing in RGB only.
Only for my portfolio-book I show to the clients - not for proofing.
I do not have a RIP software yet.

I have a lab that does GMG Contractproofs for me.
The lab wants CMYK-Files...

I want to see in advance what would be the best possible result.
I am aware that this will not be 100% what i will get later in offsetprinting.
Just want to know how it is possible to have that file printed closest to the RGB monitor softproof.......
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Old 09-25-2008, 08:39 PM
pixelzombie pixelzombie is offline
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Re: conversion of extremely saturated photos to cm

you could have the presshouse run the book with higher densities, you could also run a touchplate on that image which would mean a 5th color on press(more $) and the other alternative is hexachrome printing...
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Old 09-25-2008, 11:36 PM
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Damo77 Damo77 is offline
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Re: conversion of extremely saturated photos to cm

Quote:
Originally Posted by girlsfather View Post
When converting to cmyk, isocoated_v2.icc
Have you been told this is definitely the most accurate profile for the press? If so, do you believe it?

This thread sounds like another one for my "why large-gamut RGB colour spaces are pointless" file ...
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Old 09-26-2008, 08:45 AM
girlsfather girlsfather is offline
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Re: conversion of extremely saturated photos to cm

Quote:
Originally Posted by Damo77 View Post
Have you been told this is definitely the most accurate profile for the press? If so, do you believe it?

This thread sounds like another one for my "why large-gamut RGB colour spaces are pointless" file ...
That is the profile all the stuff is contractproofed here in germany.
The profile was created by the European Color Initiative (ECI)
as ISO 12647-2 was redefined.
The profiles are based on Fogra39L.
These profiles are used since last year and replace isocoated.icc.
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